=Brick Construction.=--In its principal features and general character of construction, the architecture of each of these three civilisations is similar, being based upon the methods that originated with the Chaldæans. These methods were the direct result of the geographic and climatic conditions of the country they inhabited. For Lower Mesopotamia, Babylonia proper, is an alluvial plain, interrupted by a single ridge of limestone hills which were sparsely covered with small trees, especially the scrub-oak. Timber and stone were scarce, while everywhere clay abounded. Accordingly, the chief material of construction was brick, shaped in wooden moulds and sun-dried. The limited amount of fuel permitted only the making of burnt bricks for special purposes: namely, the facing of the structures and the paving of the floors. And these superior bricks or tiles were frequently glazed and decorated with ornament in bright colours. Meanwhile, in Upper Mesopotamia, Assyria proper, the ground was comparatively arid and plentifully supplied with limestone. Yet such was the habit of the Assyrians to imitate the Southern kingdom in matters of civilisation, that they also relied upon sun-dried brick for construction, and employed glazed earthenware for decoration. In time, however, they came to employ stone for facing as well as for the sculpture, which was a characteristic decorative feature of the palaces. =Platforms.=--We shall see presently how the fierce heat affected the principles of architectural construction, noting in advance the means taken to provide against the periodical inundations due to the torrential rains and the overflow of the Tigris. From earlier times all important buildings were erected upon platforms, constructed of sun-dried bricks and faced with fired bricks or stone, the walls having a batter, that is to say, sloping inward. Approach to the summit was either by flights of steps or an inclined roadway that paralleled the wall--technically known as a _ramp_. Intersecting these mounds or platforms was a system of arched culverts, designed, as in modern railroad embankments, to carry off the water. In course of time, as buildings fell into decay or were replaced with newer ones by later builders, the height of the mound increased. The result is that the plain of Babylonia for 220 miles is studded with immense mounds, some of them a mile in diameter and attaining 200 feet in height, crowned with the remains of towns. Beneath these, the modern explorer, cutting down into the interior of the mound, comes upon successive stages of foundations, representing the remains of various epochs.